This invention relates to a method for controlling soft rot, bacterial seedling blight of rice and black rot by applying an Erwinia carotovora subsp. carotovora, particularly the Erwinia carotovora subsp. carotovora CGE234M403 strain (FERM BP-4328) alive to soil or plants.
Disease injuries of so-called soft rot caused by Erwinia carotovora develop in a large number of plants such as celery, head lettuce, carrot, Japanese radish, wasabi, potato, tobacco, tomato, cyclamen, etc. including Chinese cabbage and cabbage. As a method for controlling this soft rot, antibiotic preparations such as streptomycin, etc. and chemicals composed of copper compounds such as Bordeaux mixture have been mainly applied to date.
However, these chemicals not only give unsatisfactory control effects but also cause problems such as extinction of useful bacteria other than pathogenic bacteria, environmental contamination and chemical injuries. With respect to antibiotics, the appearance of bacteria having resistance to the same has become a problem.
In addition, there are a few pesticides which are now applicable to a method for controlling bacterial seedling blight of rice caused by Pseudomonas plantarii bacteria, so that a pesticide which can control the disease effectively is expected to be developed.
Furthermore, black rot caused by Xathomonas campestris pv. campestris develops in crops of Cruciferae such as cabbage, radish, broccoli, Chinese cabbage, etc. and its damage is serious. As a method for controlling this black rot, preventive spraying of copper wettable powder, organic copper wettable powder, Kasugamycin-copper wettable powder, copper hydroxy nonylbenzenesulfonate-copper wettable powder, copper-vinclozolin wettable powder and probenazole granules immediately after planting is carried out at present as a method of chemical pest control.
However, it is difficult to say that these chemicals give effective results. In addition, the appearance of resistant bacteria, environmental contamination, chemical injuries, etc. become problems. Accordingly, pesticides which are highly safe and raise no problem of environmental contamination are expected to be developed.
Erwinia carotovora is a bacterium causing so-called soft rot which softens and rots storage tissues of many plants such as Chinese cabbage, radish, etc. and is reported to exist in soil universally. Even in a field where a crop which serves as a host of this bacterium has not been grown for 5 years or more, there occasionally is a case where the occurrence of soft rot is observed. The ecological form of this bacterium is discussed in Hiroyuki Tsuyama, Shokubutsu Boeki (Plant Protection), vol. 34, pp. 294-298 (1980). In the case, for example, of Chinese cabbage, this bacterium grows around the root part of the plant on about the 40th day after seeding, and its existence comes to be observed in almost all the parts such as rhizosphere soil, top, etc. And, once chinese cabbage is injured by typhoon, insects, routine work, etc., the bacterium invades the site of injury, and if climatic conditions are right, the concentration of the pathogenic bacteria rises in only one night and lesions come to be observed. Therefore, if it becomes possible to grow nonpathogenic Erwinia carotovora instead of pathogenic ones in the rhizosphere soil and the top soil equally to the pathogenic strain, it can be expected that this will suppress the growth of the pathogenic bacterium and thus control soft rot. The present inventors made an intensive study on the basis of the above consideration. As a result of this study, they found that soft rot could be controlled effectively by selecting an Erwinia carotovora strain which not only grows well in competition with pathogenic strains of the Erwinia carotovora, but also has no pathogenicity. This strain was obtained from mutagenized strains of Erwinia carotovora and is applied to soil and plants as a microbial pesticide preparation containing this strain as an active ingredient. As a result of further studies, the inventors found that bacterial seedling blight of rice and black rot could also be controlled effectively by applying this microbial pesticide preparation to soil or plants. Thus, the inventors attained the present invention.